The invention relates to a burner with which liquid fuel is burned and, an electric heating device being used at startup for heating a fuel vaporization chamber, hot exhaust gases from burner operation being used to heat the vaporization chamber from the outside so that when a desired vaporization temperature is reached, the electric heating device can be shut down.
Such burners are advantageously used in heating systems for residential and non-residential buildings. The heat produced by the burner during the combustion of the fuel heats, for example, water in a heating boiler. In addition to burners for liquid fuels, such as heavy oil, extra light heating oil or kerosene, there are burners for gaseous fuels such as natural gas. The latter are distinguished in particular by the fact that their generation of heat can be controlled over a large output range, which in the technical world is designated modulation capacity. In addition, gas burners have favorable values with regard to pollutant emissions.
Burners for liquid fuels are widespread. Whereas burners for heavy oil are used in furnaces of industrial plants, burners for light heating oil, in particular such heating oil of the type xe2x80x9cextra light heating oilxe2x80x9d, predominate in heating systems in residential and non-residential buildings. In this case, atomizer burners are widespread, in which the heating oil delivered by an oil pump is atomized by means of a nozzle and directly burned. Such burners can only be modulated starting from higher outputs, e.g. greater than 100 kW. On account of constructional measures such as better insulation of buildings, the specific heat requirement has decreased in the last two decades. Atomizer burners are only suitable for heating systems having a rated output of 15 kW and above. If the heat requirement is lower, which is the case in newer houses for example, the burner must be switched on and off continuously, that is to say it has to run in so-called cyclic operation. However, it is known that every switch-on action is associated with an increased pollutant emission, so that less favorable emission values result overall.
For the aforesaid reasons, the relevant industry has created so-called vaporizing burners. In these burners, the fuel is vaporized by the effect of heat and then mixed with air and burned. Such burners were to begin with used mainly for the combustion of kerosene or petroleum, since these fuels have a relatively low vaporization temperature. With kerosene or petroleum as fuel, it is possible, during burner start-up, to heat the kerosene or petroleum to the vaporization temperature in the vaporizing chamber by means of an electric heating device, but to subsequently switch off the electric heating device when the heating device together with the burner has been heated up to such an extent that the vaporization of the kerosene or petroleum is maintained by the sensible heat of the heating device. With extra light heating oil, however, continuous operation of the electric heating device is necessary on account of the much higher vaporization temperature with this fuel.
FR-A1-2 733 579 discloses a burner intended for the combustion of kerosene, in which case it is questionable whether it might also be suitable for extra light heating oil. It contains the electric heating device already mentioned, which is switched on when a temperature sensor indicates the need for preheating. It cannot be clearly recognized whether it also switches off the preheating again after the burner start-up. Since the temperature sensor is also not shown, it also cannot be clearly recognized where and how it should be arranged.
DE-A1-25 34 066 discloses a burner which is more suitable for burning extra light heating oil. It contains the electric heating device already mentioned. It serves not only to heat the fuel but also to heat the air required for the combustion, so that the fuel already vaporized is prevented from condensing again. Inadequate heating would lead to the fuel not burning in a clean manner but partly carbonizing, which leads to malfunctioning after a short time.
It is also known (DE-A1-41 26 745) to first of all atomize the fuel by means of a nozzle in order to subsequently vaporize it by means of an electric heating device.
The object of the invention is to provide a burner which is suitable for burning extra light heating oil and in which the vaporizing chamber has to be heated by means of the above-mentioned electric heating device only during the starting phase when the burner is cold, whereas the supply of external energy for heating the fuel is unnecessary during the subsequent operation of the burner.
In accordance with the invention, a burner for liquid fuel is provided with an electric heating device for start up heating fuel vaporization chamber to a selected temperature, the vaporization chamber having a fuel atomization element therein. A flame retention baffle is fitted on the vaporization chamber, and a temperature sensor is provided for sensing temperature of the vaporization chamber. A fan supplies an air flow through the vaporization chamber and vaporized fuel mixes therewith and is ignited producing a flow of hot exhaust gases. At least a portion of the hot exhaust gases is deflected so that said deflected hot exhaust gases portion will heat up the vaporization chamber from the outside. When the vaporization chamber is heated to a desired temperature of about 350 degrees Celsius by the deflected hot exhaust gases from the burner operation and such temperature is sensed by the sensor the sensor outputs a signal so that the electric heating device can be shut down, vaporization chamber heating then being maintained by the deflected hot exhaust gas flow.